Power system dynamics during disturbances

The main targets of power system operation are the security and stability of the power system as well as the reliability and quality of supply to all customers in an economic manner which is a big challenge nowadays. To achieve the above targets system disturbances have to be analyzed carefully to fix all problems in the minimum possible time and avoid the repetition of the same problem again (e.g. Faults and/or generating units tripping). This paper presents the concepts of one of the effective tools for disturbance analysis used in Saudi Electricity Company in the Western Region named as Dynamic System Monitoring (DSM). It is basically a computer system connected in each station to record voltage and current as well as frequency with fast rate (240 samples per second for 60 Hz system). When any system disturbance takes place causing the trigger of one or more of the predefined triggers, each event will be saved in the computer hard disk in one or more files defined by date and time with recording duration from 20 to 30 seconds for each file. The DSM units are linked by telephone lines and modems to the Master Station PC computer located in the Head Office and each disturbance event can be retrieved and analyzed by DADISP software package working under Windows 2000, NT or XR Three actual disturbances in the Western Region are described and analyzed in details using the records of the concerned DSM units and cross checked with the records of some numerical protection relays to insure the correct operation and the technical recommendations are listed and implemented in most cases to avoid repeating the same event in future. The paper also presents a good and practical new method for the evaluation of Active Spinning Reserve (ASR) which is also called immediate reserve loadable in the first three seconds for some generating units in Saudi Electricity Company using the actual records of the Dynamic System Monitoring (DSM). In case of big generating unit trips, system frequency drops causing DSM units to trigger and record all measurements in an event file which is used to analyze that event including the dynamic behaviour of each on bar generating unit to determine its load pick up share in MW for the restoration of system frequency. Actual incidents of big generator tripping and load rejections at Shoaibah (393 MW) and at Rabigh (266 MW) Power Plants are analyzed in details using DSM records to evaluate the average (ASR) for each unit in service which is of great importance in the evaluation of total system immediate reserve to insure system security and stability. The most recent tools similar to DSM units is also listed where higher scan rates are incorporated for more accurate results.